There have conventionally been known inkjet printers that include an inkjet head having a plurality of channels that discharge ink. Such inkjet printers are capable of outputting a two-dimensional image onto a recording medium such as a sheet of paper, cloth, etc. by controlling discharging of ink while moving the inkjet head relatively with respect to the recording medium. Discharging of ink can be performed by using an actuator (a piezoelectric actuator, an electrostatic actuator, a thermal actuator, or the like), or by generating air bubbles in ink in a tube by means of heat. In particular, piezoelectric actuators have recently been widely used for their advantages of large output, modifiability, high responsiveness, adaptability to any type of ink, etc.
Piezoelectric actuators are classified into two types: one using a bulk-state piezoelectric body and the other using a thin-film piezoelectric body (piezoelectric thin film). The former type has a large output and thus is capable of discharging ink droplets of a large size, but it is large-sized and thus is high in cost unfortunately. In contrast, the latter type has a small output and thus is not capable of forming ink droplets of a large size, but is compact and thus is low in cost. Consequently, it can be said that forming an actuator with a piezoelectric thin film is suitable to realize high-resolution printers (which can be achieved with small ink droplets) at low cost.
Reference is now made to FIG. 8, which presents a plan view schematically showing a configuration of a conventional actuator 100 using a piezoelectric thin film, and a sectional view taken along line A-A′ of the plan view and viewed in the direction indicated by the arrows. The actuator 100 is configured by stacking, on a substrate 101 having a pressure chamber 101a, an insulation layer 102, a lower electrode 103, a piezoelectric film 104 as a piezoelectric thin film, and an upper electrode 105 in this order. An upper wall 101b of the pressure chamber 101a in the substrate 101 constitutes a driven film operable to be displaced according as the piezoelectric film 104 expands and contracts.
Specifically, when a voltage is applied from a drive circuit 106 to the lower electrode 103 and the upper electrode 105 and the piezoelectric film 104 is caused to expand and contract in a direction perpendicular to its thickness direction (a direction parallel to a face of the substrate 101), curvature is generated in the driven film due to difference in length between the piezoelectric film 104 and the driven film, the curvature causing the driven film to be displaced (curved) in its thickness direction.
A configuration of a channel 200 including the actuator 100 shown in FIG. 8 is schematically shown in FIG. 9, which is a sectional view. As shown in the figure, an ink chamber is formed by closing a space (the pressure chamber 101a) in a lower portion of the actuator 100 with a nozzle plate 201. With ink held in the pressure chamber 101a, by making use of the above-described displacement of the driven film caused by the expansion and contraction of the piezoelectric film 104, it is possible to apply pressure to the ink held in the pressure chamber 101a to thereby discharge the ink as ink droplets through a nozzle hole 201a to outside the pressure chamber 101a. An inkjet head is formed by arranging a plurality of such piezoelectric actuators 100 (channels 200) in a lateral direction.
Piezoelectric bodies widely used in such piezoelectric actuators as described above are perovskite metal oxides such as BaTiO3 and Pb(Ti/Zr)O3 which is called PZT. As for actuators using, a piezoelectric thin film, the piezoelectric thin film is produced by forming on a substrate a film of PZT, for example. The PZT film can be formed by means of various methods, such as a sputtering method, a CVD (chemical vapor deposition) method, a sol-gel method, and the like. Incidentally, since it requires a high temperature to crystalize piezoelectric materials, Si substrates are often used as the substrate.
Performance indices of an inkjet head include droplet amount, injection speed, drive frequency, etc., and output and responsiveness of each actuator serve as factors that determine these indices. The output of an actuator depends on the applied voltage, the piezoelectric constant, and the volume of the piezoelectric body, while the responsiveness of an actuator depends on the weight, the stiffness, etc. of the actuator.
The drive frequency of a head is also affected by weight and elasticity of ink. Specifically, with a large-capacity pressure chamber (ink chamber), which holds ink of a large weight, the ink as a whole becomes more elastically deformed, as a result of which the responsiveness of the actuator is degraded. Accordingly, to improve the responsiveness of the actuator so as to improve (increase) the drive frequency of the head, it is necessary to reduce the capacity of the ink chamber.
Methods for reducing capacity of an ink chamber include the following two methods. One is to polish a substrate, on which a piezoelectric body is supported, to reduce the height of an ink chamber formed in the substrate. The other is to transfer onto a thin substrate, in which a small-capacity ink chamber is formed in advance, a piezoelectric film formed on another substrate, thereafter removing the another substrate. Although adopted for different purposes, polishing a substrate as in the former method is disclosed in Patent Literature 1, for example, and transferring a piezoelectric film as in the latter method is disclosed in Patent Literature 2, for example.